Today, user interaction between machines and people is generally implemented by the use of conventional mechanical switches. Although the mechanical switch offers low cost, robustness, and reliability, it is not suitable, due to its mechanical moving parts that must move several millimeters, for some disabled people who cannot exert enough force to press on the switch. Another problem for the commonly used mechanical switch is that the user cannot see it at night and therefore an additional small light source is inserted in or placed along the side of some mechanical switches. The force problem in the mechanical switch can now be alleviated by using a touch switch based on surface acoustic wave technology [E. Dieulesaint, D. Royer, O. Legras, and A. Chaabi, xe2x80x9cAcoustic plate mode touch screen,xe2x80x9d Electronics Letters, Vol. 27, pp. 49-51, January 1991]. Another approach is to use a piezoelectric-based touch switch that gives a small output voltage for activating the desired electrical load when there is a mechanical force on the active area of the switch. However, a commercial piezoelectric-based touch switch requires a strong force of 3-5 Newtons and a specially designed electrical circuit to prevent a high output saturation voltage [Catalog RS Components, RS International Division, P. O. Box 99, Corby, Northants NN17 PRS, England, September 94-February ""95]. The need of using a weaker activating force can be accomplished by using capacitive-based touch switch technology [N. Platt, W. Schilling, B. Goetz, and U. Kreiter, xe2x80x9cTouch switch with flexible intermediate conductive spacer as sensor button,xe2x80x9d U.S. Pat. No. 5,917,165, Jun. 29, 1999]. Similar to the piezoelectric-based technology, this capacitive-based touch switch needs an additional electrical circuit to prevent the unwanted output voltage disturbance due to the electrostatic inductance change when the finger is approaching or touching the active area of the touch switch. Another type of touch switch is based on the use of resistive membranes that still need a typical contact movement of membrane in submillimeters in order to provide a reliable switching action and sufficient insulation between contacts [E. So, H. Zhang, and Y. -S. Guan, xe2x80x9cSensing contact with analog resistive technology,xe2x80x9d IEEE Conference on Systems, Man, and Cybernetics, Vol. 2, pp. 806-811, Japan, October 1999]. This level of mechanical movement in resistive touch switch technique also introduces a degree of wear-and-tear that limits the life of the touch switch. Furthermore, these touch switch technologies also require an additional light source embedded in the touch switch module in order to be able to use in the dark area. Hence, it would be highly desirable to have a touch switch structure where the contact switching concept is inherently based on the use of light beam.
Previously, two types of optical touch switch were proposed by means of light reflection [K. Friedrich, G. Straimer, and B. Godesberg, xe2x80x9cReflection type contactless touch switch having housing with light entrance and exit apertures opposite and facing,xe2x80x9d U.S. Pat. No. 3,621,268, Nov. 16, 1971] and light blocking methods [C. R. Fisber, xe2x80x9cOptical keyboard,xe2x80x9d U.S. Pat. No. 43,873,607, Jun. 7, 1983]. Nonetheless, the disadvantage of these previous optical touch switch structures is that more than one spatially fixed photodetectors are utilized to detect the optical beam reflected and scattered from the user""s finger. In addition, they are inappropriate for use in real life as the free-space propagating light beam emanating from the touching surface of the switch can easily hit the user""s eyes. Hence, to achieve a user-friendly optical touch switch, the present invention uses concepts of light total internal reflection (TIR) and light scattering to implement an optical touch switch. The key main idea comes from the fact that the evanescent optical field at the TIR surface can be coupled out when a component, whose refractive index is close to the index of refraction of the TIR material, is placed on the TIR surface. The scattered light is generated at this TIR surface as well. The TIR- and light scattering-based optical touch switch concepts offer several additional key advantages including ease of implementation, prevention of the light beam incident directly on the user""s eyes, and ability to accept both strong and weak mechanical activating forces. Note that since the discovery of TIR of light in 1800""s by John Tyndall [B. E. A. Saleh and M. C. Teich, Fundamentals of Photonics, John Wiley and Sons, 1991], the TIR principle has been employed in several applications including a fiber-optic communication system, an optical switch [S. K. Sheem, xe2x80x9cTotal internal reflection integrated-optics switch: a theoretical evaluation,xe2x80x9d Applied Optics, Vol. 17, No. 22, pp. 3679-3687, November 1979; R. I. MacDonald, xe2x80x9cDeflection optical matrix switch,xe2x80x9d U.S. Pat. No. 6,005,993, Dec. 21, 1999], an optical beam deflector [M. B. Chang, xe2x80x9cTotal internal reflection deflector,xe2x80x9d Applied Optics, Vol. 21, No. 21, pp. 3879-3883, November 1992], a fiber-optic hydrophone [W. B. Spillman Jr. and D. H. McMahon, xe2x80x9cFrustrated-total-internal-reflection multimode fiber-optic hydrophone,xe2x80x9d Applied Optics, Vol. 19, No. 1, pp. 113-117, January 1980], an interferometer [S. Sainov, V. Sainov, and G. Stoilov, xe2x80x9cInterferometer based on total internal reflection,xe2x80x9d Applied Optics, Vol. 34, No. 16, pp. 2848-2852, June 1995; W. Zhou and L. Cai, xe2x80x9cInterferometer for small-angle measurement based on total internal reflection,xe2x80x9d Applied Optics, Vol. 37, No. 25, pp. 5957-5963, September 1998], a fiber-optic sensor [K. Rahnavardy, V. Arya, A. Wang, and J. M. Weiss, xe2x80x9cInvestigation and application of the frustrated-total-internal-reflection phenomenon in optical fibers,xe2x80x9d Applied Optics, Vol. 36, No. 10, pp. 2183-2187, April 1997], the measurement of refractive index [H. Li and S. Xie, xe2x80x9cMeasurement method of the refractive index of biotissue by total internal reflection,xe2x80x9d Applied Optics, Vol. 35, No. 10, pp. 1793-1795, April 1996; M. -H. Chiu, J. -Y. Lee, and D. -C. Su, xe2x80x9cRefractive-index measurement based on the effects of total internal reflection and the uses of heterodyne interferometry,xe2x80x9d Applied Optics, Vol. 36, No. 13, pp. 2936-2939, May 1997], spectroscopy [J. S. Loring and D. P. Land, xe2x80x9cTheoretical determination of parameters for optimum surface specificity in overlayer attenuated-total-reflection infrared spectroscopy,xe2x80x9d Applied Optics, Vol. 37, No. 16, pp. 3515-3526, June 1998], a fingerprint input device [J. N. Monroe, xe2x80x9cFingerprint observation and recording apparatus,xe2x80x9d U.S. Pat. No. 3,527,535, Sep. 8, 1970], and microscopy [P. S. Carney and J. C. Schotland, xe2x80x9cThree-dimensional total internal reflection microscopy,xe2x80x9d Optics Letters, Vol. 26, No. 14, pp. 1072-1074, July 2001].
The present invention is directed to an optical touch switch being operated by contact that incorporates a light source for illuminating the optical touch switch module and giving the optical beam to sense the mechanical activating force applied on the touching surface of the optical touch switch; a light guide having at least one surface that the total internal reflection or light scattering can be generated; at least one photodetector for detecting light due to total internal reflection or light scattering phenomenon; imaging system for controlling the size of the optical beam and direction of light propagation; spatial filters for controlling the size of the optical beam and propagation direction of light as well as for suppressing the unwanted optical noise; and an electronic control box for sensing the change of electrical current produced by the photodetector and for controlling the electrical load connected at the output of the electronic control box.
In one embodiment of the optical touch switch, the light guide is a triangle prism. In another embodiment, the light guide is a Rhomboid prism. In another embodiment, the light guide is a Dove prism. In a further embodiment, the light guide is a penta prism or polyangle prism. In an even further embodiment, the light guide is a slab rectangular light guide made from plastic, glass, or polymer. In another embodiment, the light guide is an optical fiber made from glass, plastic, or polymer. Variations to the structure of the light guide include the light guide having at least one touching surface; the total internal reflection point along the touching surface of the light guide having at least one point; the position of light scattering along the touching surface of the light guide claim having at least one point; and the surface of the touching surface of the light guide being divided into a light diffusing area, a light blocking area, and a sensing area.
Optical touch switches are implemented based on the use of light total internal reflection and light scattering concepts. The optical touch switch basically consists of a light source, a light guide, a photodetector, and an electronic controller. The fingertip touching on the touching surface of the optical touch switch leads to the change in electrical current produced by the photodetector. As a result, the electronic control box senses this change of electrical current and allows the electrical load to stay at the desired state. Key advantages include ease of implementation, prevention of the light beam incident directly on the user""s eyes, and ability to accept both strong and weak mechanical forces from users.